A new poll from Quinnipiac University shows the Senate races in Georgia and Iowa all but decided, while the North Carolina contest remains tight.

A survey of early voting in Georgia showed challenger Jim Barksdale ahead of incumbent Republican Sen. Johnny Isakson by 1 point among voters who cast early ballots. But Isakson held a commanding 54 percent to 40 percent lead among all likely voters.

Nevada state Sen. Ruben Kihuen is the sole House Democratic recruit the Democratic National Convention Committee has touted as a major speaker in Philadelphia this week.

The selection of a Hispanic state legislator underscores Democrats’ desire to showcase diversity on stage this week, while also promoting a candidate who has a good opportunity to flip a red seat blue.

In close races, the quality of the candidates can make all the difference. And with a few notable exceptions, most incumbents acquit themselves well with strong fundraising, good campaigns, and a message tailored for victory.

So this year, Roll Call has decided to rank the Senate challengers — that is, the candidates for office who aren’t incumbents. It’s a list that leans heavily Democratic in 2016, a year when Republicans are playing defense in all but two seats currently considered at all competitive.